[Java 9] Fix GitDateFormatterTest

[Java 9] Fix GitDateFormatterTest

In JDK 9 and later, the default locale data uses data derived from the
Unicode Consortium's Common Locale Data Repository (CLDR). So there are
changes with respect to some locales.

For example the short date-time format is ‹{1}, {0}› in the CLDR locale,
as opposed to {1} {0} in the JRE locale data.

See: https://bugs.openjdk.java.net/browse/JDK-8206961
See: https://www.unicode.org/cldr/charts/29/by_type/date_&_time.gregorian.html#1141bf54834c4261
Change-Id: I7535821e8ecd8702a95db8732cbbf3a4a7385eca
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>